The present invention relates to a method and apparatus for deaeration of condensate in a power generating steam turbine plant, and, more particularly to a combined cycle plant of the type in which the condensate is deaerated in a condenser so as to permit a quick start up of the turbine plant.
Generally, in a steam turbine plant, of, for example, an electric power generation plant, it is necessary to deaerate the condensate before it is fed as the feedwater to the boiler, in order to prevent the boiler from being corroded by the gases, particularly oxygen, dissolved in the condensate. The oxygen content of the condensate in the condenser of such plants is generally high and well reaches a very high value of 7000 ppb at the maximum particularly when the plant is not operating. On the other hand, in order to prevent the corrosion of the boiler, it is required that the oxygen content of the feedwater is on the order of 5 to 10 ppb. When the plant is started, therefore, it is necessary to deaerate the condensate to decrease the oxygen content to the required low level. To this end, steam turbine plant is usually provided with a deaerator for deaerating the condensate before the condensate is fed as the feedwater to the boiler. In some types of power generating plants, however, the deaerator is omitted and the deaeration of the condensate is made by the deaeration effect produced by the condenser. An example of such types of the steam turbine plant is the combined cycle in which the cycle efficiency of steam turbine is improved by an efficient use of heat wasted from a gas turbine. In such a steam turbine plant, therefore, a considerably long time is required for deaerating the boiler feedwater, i.e. the condensate, to reduce the oxygen content to the required level to make it difficult to quickly start up the plant as a whole.
In order to overcome this problem, it has been proposed that the condensate from the condenser is recycled to the condenser, while the inside of the condenser is depressurized to a vacuum by an air ejector and auxiliary steam is introduced into the condenser to heat the condensate, to thereby promote the deaeration by the condenser. This measure, however, is still unsatisfactory in that a long period of time is required for the recirculation of the condensate thereby impeding the quick start up of the plant, although the time length required for the start up is shortened to some extent. This problem is serious particulary in the case of power generating steam turbine plant of the combined cycle type. Namely, such type of steam turbine plant cannot cope with the demand for the quick start up although it is required to operate as a middle plant from the view point of the performance thereof.
Another solution to this problem is proposed in Japanese Patent Laid-Open No. 112811/1980 , wherein a storage tank is employed for storing deaerated condensate and a storage tank for storing make-up water before deaeration. In the beginning period of starting up of the steam turbine plant, the deaerated condensate is supplied from the first-mentioned tank to the boiler, while the make-up water is recycled between the condenser and the second-mentioned tank so as to be progressively deaerated. When the oxygen content of the water in the condenser has come down to the required low level, the feedwater line to the boiler is switched to the normal line. This method, however, cannot speedup the starting of the plant because the deaeration is made through recirculating of the make-up water. In addition, since the feedwater is supplied from the first-mentioned tank for storing deaerated condensate for a long time until the make-up water in the condenser is deaerated sufficiently, the tank is required to have an impratically large capacity.
Accordingly, an object of the invention is to provide, in a power generating steam turbine plant in which the condensate is deaerated by a condenser, a deaeration method which permits a quick deaeration of the condensate and, hence, a quick start up of the steam turbine plant.
Another object of the invention is to provide a condensate deaeration method which permits a quick start up of a power generating steam turbine plant of condenser deaeration type, particularly combined cycle plant, capable of realizing a diversification of operation of the power generating plant.
Still another embodiment of the invention is to provide a condensate deaeration apparatus suitable for use in carrying out the above-mentioned method.
A further object of the invention is to provide a condensate deaeration apparatus which can remarkably shorten the time required for starting up of the turbine plant at a low cost, without requiring substantial change in the construction of the conventional power generating steam turbine plant.
To this end, according to one aspect of the invention, a condensate deaerating method is provided for use in starting at least one power generating steam turbine plant, wherein before starting up the plant, a condensate is substituted in an equipment possessing deaerated condensate for the condensate in the condenser of the plant to be started and the substituted condensate is supplied to the boiler, to thereby permit a quick start up of the steam turbine plant.
According to another aspect of the invention, a condensate deaeration apparatus for use in a system having a plurality of power generating steam turbine plants is provided which includes a first communication means for providing a communication between the plants and is adapted to introduce deaerated condensate from the condenser of at least one of the plants under operation to the condenser of at least one of the plants which is to be started. A second communication means provides a communication between the plants and is adapted to introduce non-deaerated condensate from the condenser of the at least one of the plants to be started to the condenser of the at least one of plants under operation. A valve means selectively operates the first and second communication means, whereby the non-deaerated condensate possessed by the condenser of the plant to be started is substituted by the deaerated condensate possessed by the condenser of the plant under operation, to thereby permit a quick deaeration of the condensate in the plant to be started.